Internal members for mass transfer columns

ABSTRACT

Internal members or baffles for material exchange columns have at least one packing bed. The packing bed has at least one first packing block and at least one correction element associated with the first packing block. The first packing block and its associated correction element produce different final distributions of liquid or systematic maldistributions. The systematic maldistribution in the liquid phase caused by the first packing block is largely corrected by the systematic maldistribution of the associated correction element. Such an arrangement makes possible enhanced separation efficiency or higher packing beds.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/CH98/00293 which has an Internationalfiling date of Jul. 3, 1998 which designated the United States ofAmerica.

TECHNICAL AREA

The present invention concerns internal members or baffles for masstransfer columns, also called column baffles. The invention relates inparticular to packing that serve the purpose of mass transfer between aliquid and a gaseous or vapor phase.

STATE OF THE ART

Internal members, also described column baffles, are used in variousapplications both in thermal separation technology and in mixingtechnology for mass transfers and heat exchanges between twofluid-phases. They can be installed as separating or mixing members incolumns and similar devices, which are used, among other things, fordistillation, rectification, sorption, reaction or extraction. In thecase of thermal and mass transfer/exchange between a liquid and agaseous or vapor phase, the members' purpose consists of distributingthe gas or vapor and the fluid, which can either flow through the columnin the opposite direction of the gas or vapor flow or in the samedirection, evenly across the column cross-section and to create as largea liquid surface as possible for mass and thermal transfer/exchange.Plates and/or packings are used as column members. Over the classicplate column, packed columns, i.e. columns whose members consist ofpackings, offer particular benefits with regard to pressure dropthroughout the column, the flow rate and thus also the low thermalstress for sensitive substances. As far as investment costs areconcerned, packed columns are usually considerably less expensive thanplate columns due to the smaller building volume that is required.

Apart from so-called random packings, structured packings are also beingused increasingly as packings for mass transfer columns. When used indistillation columns, structured packings offer especially greatbenefits in the areas of separation efficiency and increased scalingtowards columns with larger diameters as compared to random packings.

Due to their structure, structured packings can be divided further intoa “corrugated surface” type and a “grid packing” type. Packings of thecorrugated surface type have plates that are crimped in a criss-crossingpattern, which are installed as paraxial members in the columns, andthey create only one preferred direction that is recognizable in thecross-section projection of the column due to their structure of the gasor vapor flow as well as the fluid flow for one packing element each. Atypically structured packing of the corrugated surface type is shown inDE 26 01 890.

Contrary to this, structured packings of the grid packing type have agrid-shaped, open structure, and the grid elements (lamellae or partialareas) are arranged in a net, grid or fan shape. The grid elements areconnected on cross or knot areas, with arrangements possible intwo-dimensional or three-dimensional form. Structured packings of thegrid packing type can create more than one preferred direction that isrecognizable in the cross-section projection of the column due to theirstructure of the gas or vapor flow and/or the fluid flow for one packingelement each. For a suitable grid packing's design or structure evencrimped sheets can be used to set up this packing type. A typicalstructured packing of the grid packing type is the one described in EP069 241, which is sold under the “Rombopak” brand name.

Structured packings of the corrugated surface type have the advantage ofa simpler production procedure over those of the grid packing type.However, due to connected surfaces (closed structure), the disadvantagearises that for structured packings of the corrugated surface type,lower wetting of the packing surface is achieved and thus also a smallerfluid surface for the mass transfer and heat exchange than is the casewith grid packings. Therefore, higher efficiency in the separation canbe achieved with separation columns equipped with structured packings ofthe grid packing type than can be achieved with separation columnsequipped with packings of the corrugated surface type.

In applications with high purity requirements, however, the utilizationof packed rectification columns still meets with resistance in theindustry because the maldistribution problem, especially in the fluidphase, occurs both with random packings and structured packings.Maldistribution manifests itself through the fact that a fluid flow,which initially is evenly distributed over the cross-section of thecolumn, displays uneven final fluid distribution after having passedthrough the packing. The separation efficiency's quality, however,depends on the evenness of the gas or vapor and fluid over the entirecross-section of the column's interior along the flow path and theintensity of its mixing process. The maldistributions occurring in thefluid and vapor flows can be divided into two different maldistributiontypes. Stochastic maldistribution describes a (random) small-scalemaldistribution. Over large surface areas, distribution evens out.Systematic maldistribution, on the other hand, characterizes alarge-scale maldistribution in relation to the column cross-section. Inindustrial reality, stochastic maldistribution is always superimposed onsystematic maldistribution.

A special type of stochastic maldistribution is the insufficient, roughpre-distribution of the fluid above a packing bed. Over a large surfacethe fluid flow is evenly distributed, i.e., into a certain number ofevenly distributed partial fluid flows of the same kind, generated bythe fluid distributor that is utilized. Over a small surface, however,maldistribution occurs, i.e., surface areas without fluid supply andareas where there is a fluid flow of the distributor. This type ofstochastic maldistribution due to insufficient pre-distribution of thefluid can be improved through sophisticated distributors or additionaldistribution aids.

From DE 44 18 488, we know that an increased flow of fluid and vaporoccurs in the area of the column wall—the so-called wall effect, aspecial type of systematic maldistribution —since the random packing'sor packing's wall layer offers lower resistance. In these areas, thefluid participates insufficiently in mass transfer. According to thearticle “Problems and Experiences with Large Technical Packing Columns,Chem.-Eng.-Tech. 64 (1992), No. 1, pages 6-16” by Martin Gann et al., itis true that, due to their structure, structured packings run a lowerrisk of systematic maldistribution than random packings, however theyare not—as previously assumed—self-distributing.

In particular systematic maldistribution in the fluid and vapor flowcauses negative effects on separation efficiency because balanced mixingover the column cross-section is not ensured. In the case of stochasticmaldistribution on the other hand, more or less distinct cross-mixingcan continuously balance and compensate for the negative influence.

As can be seen, among other things, from DE 44 18 488, packingmanufacturers recommend multiple collection of the fluid and itsredistribution over intermediate distributors as a common remedy formaldistribution. To achieve this, the packing is divided into severalbeds between which the fluid collector and the intermediate distributorare arranged. This measure is beneficial for both types ofmaldistribution mentioned above; mainly, however, to eliminatesystematic maldistribution. In the utilization of fluid collectors anddistributors, however, their cost and the increased building height ofthe columns proved to be disadvantageous.

To avoid the sophisticated collector and intermediate distributormentioned above, attempts have been made to utilize distributionelements which include the function of both collecting andredistributing the fluid. U.S. Pat. No. 5,523,062A (Chemical Research &Licensing Company) deals with such a combined distribution element foreven distribution of gas and liquid flow, which is suited for acatalytic distillation column. The zigzag-shaped distribution element isarranged crosswise between the packing elements, with flow openings forthe gas and fluid being arranged exclusively at the peaks and valleys ofthe zigzag (corrugated) structure. Unfortunately, it was shown that suchcombined redistribution devices are not very effective. First the fluidis not mixed completely, and second an even degree of distribution isvery difficult to achieve.

To improve and compensate for stochastic maldistribution, it wassuggested to arrange distribution elements on both limitations of apacking bed (top and bottom), but also between the packing beds:

U.S. Pat. No. 4,842,778 A (Glitsch Inc.) suggests arranging threedistribution elements each on the upper and lower ends of a packing bedat a low height, whose primary function would consist of improving theinitial distribution of the gas and fluid flow. The distributionelements consist of the “corrugated surface” packing type. They can alsobe arranged within a packing bed to reinforce the even and unifieddistribution of fluid and vapor. Installation of multiple distributionelements, moreover, strives to eliminate separate fluid and vapordistributors.

SU 1 681 924 A (Stytsenko) recommends arranging one or more distributionelements (or redistribution packings) at the beginning of a packingimmediately after the fluid distributor, but also within a packing bed,to distribute the fluid flow more evenly. This causes secondarydistribution of the fluid after the distributor and/or avoids localirregularities (stochastic maldistribution). In this case, both thepacking and the redistribution packages are the “corrugated surface”type.

In DE 44 18 448 a procedure and device are suggested as an improvedsolution for overcoming the systematic maldistribution problem createdin particular from the wall effect, wherein an intended maldistributionof the fluid dripping density is created above the column cross-sectionby appropriately designing the fluid distributor in order to compensatefor systematic maldistribution of the liquid phase generated by thefollowing packing bed. Intensive examinations and numerous testsperformed by the applicant of the present invention have shown, however,that the solution according to DE 44 18 488 does not solve the problemof systematic maldistribution, but only shifts it locally. While theevenness of fluid distribution is good on the top and poor on the bottomwithout well-aimed maldistribution of the fluid dripping density on theupper end of a packing bed, intentional maldistribution of the fluiddripping density causes the evenness of the fluid distribution to bepoor on the top and good on the bottom.

WO 97/16247 A (Sulzer) recommends arranging neighboring packing elementsat a distance to each other to reduce the pressure drop in the vaporflow and to arrange so-called fluid control means in the space betweenneighboring packing elements. The only result of this, however, iscontrolled drainage of the fluid and channeling to the next lowerpacking. In particular, accumulation of the fluid on the lower packingedge of the upper packing, respectively, and the thus-generatedmaldistribution are to be avoided.

According to the article by Martin Gann et al. mentioned above, theproblem of systematic maldistribution for packings is aggravated by theso-called “scale up”, i.e. enlargement of the columns from a laboratoryor pilot scale to a large technical scale because both random packingsand structured packings are missing exactly defined fluid channeling asclassic column plates do. During “scale-up” from a laboratory or pilotcolumn to a large technical rectification column difficulties arise,especially in estimating the separation efficiency of random packings,because generally different packing sizes are used. Although thisproblem is reduced with structured packings, it nevertheless continuesto exist.

PRESENTATION OF THE INVENTION

It is the object of the present invention to make available internalelements for mass transfer columns with which the known disadvantagesassociated with the phenomenon of systematic maldistribution occurringon packings are avoided and which thus allow high packing beds with highseparation efficiency.

According to the invention, internal elements for mass transfer columnsconsist of at least one packing bed, which has at least one firstpacking block and at least one correction element assigned to the block,with the first packing block and its assigned correction elementgenerating different final fluid distributions, i.e., differentsystematic maldistributions, and the packing block and its assignedcorrection element being arranged and selected in such a way thatsystematic maldistribution of the liquid phase generated by the packingblock is corrected at least in part by that of the assigned correctionelement.

The invention is based on the known fact that, on the one hand, acharacteristic distribution of the fluid is created on column packings(in particular for random packings, but also with structured packings)after a certain packing height, which can change its extent, but not itsbasic pattern (characteristic final distribution for column packing).Based on the terminology explained above, this characteristic finaldistribution is a systematic maldistribution. On the other hand, theinvention proceeds from new knowledge according to which—contrary to awidely held opinion among experts—in the case of structured packings ofthe grid packing type, it is not an increased fluid flow that isgenerated in the area of the column wall as on other packing types, theso-called wall effect, but rather a weakened fluid flow, the so-calledwall depletion.

In the following description and claims, various terms are used for thedifferent parts of columns internal elements whose meanings areexplained here for clarification and respective limitation purposes:

A packing element describes a generally cylindrical element of thepacking with the diameter of the column, which is usually produced instandard heights of 200 to 250 mm.

A packing block is a sequence of one or more packing elements of thesame kind that are arranged immediately on top of each other. Contraryto packing beds defined below, a packing block is not interrupted bypacking elements of a different kind or by fluid control means.

Packing type is the (uniform) type of a packing block or a packingelement, e.g., random packing, grid packing, corrugated surface, etc.

A generally cylindrical element with the column's diameter, whose maintask consists of conducting the fluid phase in the column, i.e.,generating regular, specific fluid distribution after having passedthrough, or on occasion intentional systematic maldistribution, isdescribed as a fluid control means. Contrary to this, the main task of apacking element consists in creating as large a mass transfer surface aspossible and in maintaining an evenly distributed fluid and vapor flow.

Correction element is an element for the correction of systematicmaldistribution of the liquid phase flowing through the column bygenerating a specific final fluid distribution or intended systematicmaldistribution; it may consist of a packing block or a fluid controlmeans.

The sequence of at least one packing block and, if so selected, furtherpacking blocks and/or correction elements arranged on top of each other,which is not interrupted by a fluid collector, is described as a packingbed. A packing bed can have packing blocks of different packing typesand fluid control means.

Column internal elements are a sequence of one or more packing bedsarranged on top of each other.

In a very simple version of the invention, the correction elementconsists of only one fluid control means. Since fluid control means canbe built at a very small height, this version or the invention offersthe advantage that the height of the correction element is very smallcompared to the total packing height. One possible very simple versionof a fluid control means is the arrangement of concentric cone-shapedsurfaces, which channel the fluid away from the column wall or towardsit. This way, it is possible to correct wall effects or wall depletionof a packing.

In a particularly preferred version of the present invention, thecorrection element that is assigned to the first packing block consistsof a second packing block, with the first packing block and the secondpacking block of the correction element being of different packingtypes. This version of the invention is characterized by the fact thatthe entire packing bed is suited and designed for mass transfer, withoutwasting unproductive height for correction elements. Compared to fluidcontrol means, this version also offers considerable cost benefits. In apreferred version, the first packing block and the second packing blockof the assigned correction element are selected with regard to theirpacking type in such a way that a wall effect is created on one of thetwo packing blocks and wall depletion of the fluid flow on the other:i.e. two opposite, special forms of systematic maldistribution. This isthe case, for example, when packing elements of the grid packing typeare chosen for the first packing block and packing elements of thecorrugated surface or random packing type are selected for the secondpacking block of the assigned correction element, or vice versa.

The total height of packing blocks of the first packing block type (mainpacking part) preferably exceeds that of packing blocks of the secondpacking block type (correction packing part) to a considerable extent.This version of the present invention proves particularly beneficialwhen the packing type of the correction packing part displaysdisadvantages over the packing type of the main packing part; forexample, with regard to production cost or separation efficiency. At asmaller total height of the correction packing part compared to the mainpacking part, the correction packing part's disadvantages have a smallereffect on the entire packing bed. However, the overall height of thecorrection packing part and its arrangement within the main packing partmust be selected in such a way that the generated systematicmaldistribution is largely compensated for. In a preferred version ofthe present invention, the main packing part is at least three times ashigh as the correction packing part; particularly preferred is a heightthat is six to ten times that of the correction packing part, with thehigh packing beds of the main packing part being divided by severalblocks of the correction packing.

In a particularly preferred version of the present invention, the mainpacking part is of the grid packing type and the correction packing partof the corrugated surface type because in this case both of them arestructured packing types. This leads to high separation efficiency and ahigh throughput, for example, when applied to a rectification column.This version of the present invention also proves particularlybeneficial with regard to the gas or vapor flow because, on the onehand, packing blocks of the grid packing type (as well as those of therandom packing type) lead to a equalizing of the gas flow and thusfunction to align the gas flow and, on the other hand, packing blocks ofthe corrugated surface type increase the mixing effect in the gas flow.This also reduces the damaging effects of maldistribution on separationefficiency.

Furthermore, it is preferred that the first packing block and itsassigned correction element have basically the same hydraulic capacity(expressed as the flooding point or flooding limit) so that thehydraulic capacity of the total packing bed is not limited by that ofthe correction element. For the version with a main packing part andcorrection packing part in applications for rectification or absorptioncolumns, it is beneficial for similar reasons if the correction packingpart's properties do not differ considerably from those of the mainpacking part with regard to separation efficiency and pressure drop. Inthe above-mentioned particularly preferred version, the correctionpacking part therefore has roughly the same specific packing surface(i.e., approximately the same packing density) as the main packing part.

In another preferred version of the present invention, at least one ofthe first and/or other packing blocks consists of packing elements ofthe kind that creates a recognizable preferred direction in thehorizontal cross-section projection of the column due to the structureof the gas or vapor flow and/or fluid flow, with the packing elements ofthis block being arranged in an angularly rotated vertical sequence toeach other around the column axis. In the particularly preferred versionof the present invention mentioned above, with one main packing part ofthe grid packing type and one correction packing part of the corrugatedsurface type, the packing blocks each consist of partial blocks of twopacking elements, which preferably are rotated at a 90° angle relativeto one another around the column axis.

Another version that is especially attractive with regard to itsinvestment costs is the combination of random packings as the mainpacking part with grid packing as the correction packing part. Thisallows the utilization of tower packing, even with large columndiameters and raised packing beds, especially for simple separationproblems or also for contaminating fluids that contain solid matters.

Apart from the above-mentioned versions of the present invention,further beneficial sandwiching combinations of packing blocks of variouspacking types are possible, depending on the application, to reduce thefluid's systematic maldistribution generated by the packing blocksthrough appropriate combinations of different final fluid distributionsof the individual packing types. Also worth mentioning are, inparticular, alternating sequences of two packing elements each of thegrid packing type and two each of the corrugated surface type ofapproximately the same height. Finally, it is also feasible to usealternating sequences of only one packing element. This should be usedwhen various packing types that differ in their final fluid distributionhave nearly the same values regarding separation efficiency, pressuredrop and capacity.

The following detailed description, with reference to the encloseddrawings, is merely intended to provide an example for a betterunderstanding of the invention and is not to be regarded as a limitationof the scope of protection of the present invention as described in thepatent claims. An expert will easily recognize further advantageousversions and combinations of features from the following description,combined with the enclosed drawings and the patent claims; theseversions, however, are still within the limits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate a mass transfer column according to the currentstate of the art as well as preferred versions of the present invention.More particularly:

FIG. 1 Illustrates a mass transfer column according to the current stateof the art;

FIG. 2a is a diagram representing liquid load along the column diameterfor different packing types (characteristic final fluid distribution orsystematic maldistribution);

FIG. 2b is a diagram of stochastic final fluid distribution along acolumn diameter;

FIG. 3 is a view of internal members for mass transfer columns accordingto a particularly preferred embodiment of the present invention,consisting of a main packing part of the grid packing type and acorrection packing part of the corrugated surface type;

FIG. 4 illustrates internal members for mass transfer column accordingto a different embodiment of the present invention, consisting of analternating sequence of two packing elements each of the grid packingtype and two packing elements each of the corrugated surface type of thesame height; and

FIG. 5 is a partial view of internal members for mass transfer columnsaccording to another preferred version of the present invention,consisting of a main packing part of the random packing type and acorrection packing part of the grid packing type.

As a rule, the same parts are marked with the same reference numbers inthe figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a mass transfer column suitable for distillation orrectification—i.e. a distillation column—with column members dividedinto packing beds 1, 11, 21 according to the known state of the art. Forstructured packings, the packing beds 1, 11, 21 consist of individualpacking elements that are arranged on top of each other. The fluid thatis to be separated is fed into the distillation column through the fluidsupply 2. Together with fluid trickling down from the packing bed 1located above, the supply is distributed evenly over the cross-sectionof the column, or its packing bed 11, via a fluid distributor 16. Thefluid flows through the packing beds 11, 21 in the column interior downtoward the fluid drainage 4, through which the fluid, enriched with theless volatile components from the distillation column, exits as a bottomproduct. In the packing beds 11, 21 the liquid phase comes into intimatecontact with a gaseous or vapor phase, which is created by vaporizing apart of the bottom product and flows through the gas or vapor supply 3into the column, up through the packing beds 21, 11, 1 and out of thecolumn through the gas or vapor outlet 5, enriched with the morevolatile materials. During rectification, part of the overhead productsflowing out through the gas or vapor outlet 5 are condensed and fed backinto the column interior as reflux 8, where it is distributed evenlyover the cross-section of the packing bed 1 via a fluid distributor 6and flows downward through the packing bed 1.

As a remedy against maldistribution caused by the packing, in particularsystematic maldistribution, as well as for the distribution of thesupply 2, internal members of the column are divided into severalpacking beds 1, 11, 21. On the lower end of each packing bed 1, 11(except for the one on the very bottom) the fluid is gathered by a fluidcollector 7, 17 and re-distributed evenly over the cross-section of thecolumn or the packing beds 11, 21 via a fluid distributor 16, 26 so thatthere is even fluid distribution optimal for distillation at least onthe upper end of the following packing bed 11 and 21.

As soon as the fluid has covered a certain length in the packing bed 1,11, 21 underneath the fluid distributor 6, 16, 26, it is no longercompletely evenly distributed over the column cross-section due to theeffect of the packing bed 1, 11, 21 which negatively influences thedistillation column's separation efficiency. This phenomenon ofmaldistribution is shown in FIGS. 2a and 2 b for various packing types.In FIGS. 2a and 2 b, the local liquid load along the diameter (x-axis)through a mass transfer column is shown on the y-axis. The sketches inFIG. 2a depict above-mentioned final distribution, or systematicmaldistribution, which is characteristic for the respective columnpacking. Curve 111 shows the typical diagram of a packing bed of therandom packing type, curve 112 the diagram of a packing bed of thecorrugated surface type, and curve 113 the diagram of a packing bed ofthe grid packing type. Diagrams 111 and 112 show that systematicmaldistribution of fluid manifests itself in the form of wall effect forpacking beds of the random packing and corrugated surface type, with thewall effect for random packing being much more distinct than that ofcorrugated surface packing. Diagram 113 shows that systematicmaldistribution of fluid manifests itself in the form of wall depletionfor packing beds of the grid packing type. When selecting theappropriate packing height, the extent of wall depletion correspondsroughly to the extent (with reversed sign) of wall effect for corrugatedsurface types. Similarly, FIG. 2b depicts stochastic maldistribution.The sketch shows that even distribution is achieved when averaging thefluid load over larger partial areas.

In the partial view of a packing bed 201 according to a particularlypreferred version of the present invention depicted in FIG. 3, theproperties of packings of the grid packing and the corrugated surfacetype, which can be seen in FIG. 2a, are utilized. The packing bed 201according to this version of the invention consists of a first packingblock 208 of the grid packing type, following by a packing block 209 ofthe corrugated surface type, a packing block 218 of the grid packingtype, a packing block 219 of the corrugated surface type, and a packingblock 228 of the grid packing type. Therefore the packing bed 201 is asequence of three packing blocks (208, 218, 228) of the grid packingtype (main packing part) and two packing blocks (209, 219) of thecorrugated surface type (correction packing part) arranged in betweenthem.

The packing blocks 209, 219 of the corrugated surface type of thecorrection packing part consist of two packing elements each per packingblock, which are rotated at 90° relative to one another around thecolumn axis. In the distillation column shown in FIG. 3, the correctionpacking part has approximately the same specific packing surface (i.e.,about the same packing density) as the main packing part. Furthermore,the correction packing part has roughly the same hydraulic capacity(expressed as flooding point or flooding limit) and separationefficiency as the main packing part. The main packing part's height isat least three times that of the correction packing part, preferably sixto ten times greater.

Due to the final fluid distribution recognizable from FIG. 2a,systematic maldistributions of the fluid, which are caused by the mainpacking part and the correction packing part, are largely compensatedfor. In tests conducted with a distillation column according to thispreferred version of the invention, separation efficiencies considerablyhigher than 30 theoretical separation stages were achieved for onepacking bed. With the present invention, high bed heights can berealized with high separation stage numbers, which according to thestate of the art had to be divided further with the help of fluidcollectors and distributors (see FIG. 1, two lower packing beds).

During another test conducted with a distillation column in accordancewith FIG. 3, the separation efficiency of a 3.5 m-high packing bedwithout correction packing part was compared to that of a 7.5 m-highpacking bed, one arranged according to FIG. 3 and one arranged the sameway; however, additional packing elements of the grid packing type wereused instead of the packing elements of the corrugated surface type sothat the packing consisted of only one main packing part instead of amain packing part and a correction packing part. The test showed thatwithout the correction packing part the separation efficiency per bedheight decreased considerably on the 7.5 m-high packing bed compared tothe 3.5 m-high packing bed, while it remained unchanged or decreasedonly slightly with the correction packing part.

FIG. 4 depicts a mass transfer column of a different preferred versionof the present invention. The packing beds 301, 311 consist of analternating sequence of a first packing block 302, 312 out of twopacking elements of the grid packing type and an assigned correctionelement 303, 313, consisting of two packing elements of the corrugatedsurface type of about the same height as the elements of the firstpacking blocks 302, 312, followed by packing blocks 304-308, 314-320, ofthe grid packing type and the corrugated surface type respectively.

The mass transfer column in accordance with the version of the inventionshown in FIG. 5 has a packing bed 401, which consists of a first packingblock 402 of the main packing part of the random packing type, anotherpacking block 403 of the correction packing part of the grid packingtype, and a third packing block 404 of the main packing part of therandom packing type. The investment costs for a packing bed 401according to the version of the invention shown here are considerablylower than those for a packing bed 201 because only the comparativelysmall correction packing part 403 consists of relatively expensivepacking elements of the grid packing type, while the much larger mainpacking part 402, 404 consists of less expensive random packings.

In summary, it should be noted that the invention provides internalmembers for mass transfer columns wherein the known phenomenon ofsystematic maldistribution of fluids occurring on packings is suppressedconsiderably, resulting in the advantages mentioned earlier.

What is claimed is:
 1. Internal members for a mass transfer column, saidcolumn comprising at least one packing bed, said packing bed comprisingat least a first packing block and at least one correction elementassociated with the first packing block, wherein said correction elementcomprises at least a second packing block, said first packing block andsaid second packing block being of different packing types, and saidfirst and second packing blocks generate different systematicmaldistribution in the liquid phase, the systematic maldistribution inthe liquid phase generated by said second packing block substantiallycompensating for the maldistribution in the liquid phase of the firstpacking block.
 2. Internal members according to claim 1, wherein thesystematic maldistribution of one of said first and second blocks is awall effect and the systematic maldistribution of the other said packingblock is a wall depletion.
 3. Internal members according to claim 1,wherein one of said first and second packing blocks is of a packing typethat mainly equalizes the gaseous and vapor flow and the other saidpacking block is a packing type that mainly causes a mixing in thegaseous or vapor flow.
 4. Internal members according to claim 1, whereinsaid first and second packing blocks are selected from the groupconsisting of grid packing type and corrugated surface packing type. 5.Internal members according to claim 1, wherein said first and secondpacking blocks are selected from the group consisting of random packingtype and grid packing type.
 6. Internal members according to claim 1,wherein at least one of said first and second packing blocks consists ofpacking elements that create a preferred direction of the gas or vaporflow or the fluid flow in the horizontal cross-section projection of thecolumn through their structure.
 7. Internal members according to claim6, wherein the packing elements which create a preferred direction offlow are rotated 90° to one another around a column axis.
 8. Internalmembers according to claim 1, wherein said first packing block hasapproximately the same hydraulic capacity as said second packing block.9. Internal members according to claim 1, wherein the height of a mainpacking part consisting of packing blocks of the packing type of saidfirst packing block considerably exceeds the packing height of acorrection packing part consisting of packing blocks of the packing typeof said second packing block.
 10. Internal members according to claim 9,wherein said main packing part is six to ten times as high as saidcorrection packing part.
 11. Internal members for a mass transfer columncomprising at least one packing bed, said packing bed comprising atleast one first packing block and at least one correction elementassociated with the first packing block, wherein said correction elementcomprises at least a second packing block, said first and second packingblocks being of different packing types, said first and second packingblocks having approximately the same hydraulic capacity, and said firstand second packing blocks generate respectively different systematicmaldistribution in the liquid phase, the systematic maldistribution ofthe second packing block compensating for the systematic maldistributionof the first packing block.
 12. Internal members according to claim 11,wherein the systematic maldistribution of one of said first and secondpacking blocks is a wall effect and the systematic maldistribution ofthe other of said packing blocks is a wall depletion.
 13. Internalmembers according to claim 11, wherein one of said first and secondpacking blocks is of a packing type that mainly equalizes the gaseousand vapor flow and the other said packing block is a packing type is apacking type that mainly causes a mixing in the gaseous or vapor flow.14. Internal members according to claim 11, wherein said first andsecond packing blocks are selected from the group consisting of gridpacking type and corrugated surface packing type.
 15. Internal membersaccording to claim 11, wherein said first and second packing blocks areselected from the group consisting of random packing type and gridpacking type.
 16. Internal members according to claim 11, wherein atleast one of said first and second packing blocks consists of packingelements that create a preferred direction of the gas or vapor flow orthe fluid flow in the horizontal cross-section projection of the columnthrough their structure.
 17. Internal members according to claim 16,wherein the packing elements which create a preferred direction of floware rotated 90° to one another around a column axis.
 18. Internalmembers according to claim 11, wherein a main packing part consists ofpacking blocks of the packing type of said first packing block, saidmain packing part having a height that exceeds the packing height of acorrection packing part which consists of packing blocks of the packingtype of said second packing block.
 19. Internal members according toclaim 18, wherein said main packing part is six to ten times as high assaid correction packing part.
 20. Internal members for a mass transfercolumn, said column comprising at least one packing bed, said packingbed comprising at least a first packing block and at least onecorrection element associated with the first packing block, wherein saidcorrection element comprises at least a second packing block, said firstpacking block and said second packing block being of different packingtypes, said first and second packing blocks having approximately equalseparation efficiency, and said first and second packing blocks generatedifferent systematic maldistribution in the liquid phase, the systematicmaldistribution in the liquid phase generated by said second packingblock substantially compensating for the maldistribution in the liquidphase of the first packing block.
 21. Internal members according toclaim 20, wherein the systematic maldistribution of one of said firstand second blocks is a wall effect and the systematic maldistribution ofthe other said packing block is a wall depletion.
 22. Internal membersaccording to claim 20, wherein one of said first and second packingblocks is of a packing type that mainly equalizes the gaseous and vaporflow and the other said packing block is a packing type that mainlycauses a mixing in the gaseous or vapor flow.
 23. Internal membersaccording to claim 20, wherein said first and second packing blocks areselected from the group consisting of grid packing type and corrugatedsurface packing type.
 24. Internal members according to claim 20,wherein said first and second packing blocks are selected from the groupconsisting of random packing type and grid packing type.
 25. Internalmembers according to claim 20, wherein at least one of said first andsecond packing blocks consists of packing elements that create apreferred direction of the gas or vapor flow or the fluid flow in thehorizontal cross-section projection of the column through theirstructure.
 26. Internal members according to claim 25, wherein thepacking elements which create a preferred direction of flow are rotated90° to one another around a column axis.
 27. Internal members accordingto claim 20, wherein said first packing block has approximately the samehydraulic capacity as said second packing block.
 28. Internal membersaccording to claim 20, wherein the height of a main packing partconsisting of packing blocks of the packing type of said first packingblock considerably exceeds the packing height of a correction packingpart consisting of packing blocks of the packing type of said secondpacking block.
 29. Internal members according to claim 28, wherein saidmain packing part is six to ten times as high as said correction packingpart.
 30. Internal members for a mass transfer column comprising atleast one packing bed, said packing bed comprising at least one firstpacking block and at least one correction element associated with thefirst packing block, wherein said correction element comprises at leasta second packing block, said first and second packing blocks being ofdifferent packing types, said first and second packing blocks havingapproximately equal separation efficiency and approximately the samehydraulic capacity, and said first and second packing blocks generaterespectively different systematic maldistribution in the liquid phase,the systematic maldistribution of the second packing block compensatingfor the systematic maldistribution of the first packing block. 31.Internal members according to claim 30, wherein the systematicmaldistribution of one of said first and second packing blocks is a walleffect and the systematic maldistribution of the other of said packingblocks is a wall depletion.
 32. Internal members according to claim 30,wherein one of said first and second packing blocks is of a packing typethat mainly equalizes the gaseous and vapor flow and the other saidpacking block is a packing type is a packing type that mainly causes amixing in the gaseous or vapor flow.
 33. Internal members according toclaim 30, wherein said first and second packing blocks are selected fromthe group consisting of grid packing type and corrugated surface packingtype.
 34. Internal members according to claim 30, wherein said first andsecond packing blocks are selected from the group consisting of randompacking type and grid packing type.
 35. Internal members according toclaim 30, wherein at least one of said first and second packing blocksconsists of packing elements that create a preferred direction of thegas or vapor flow or the fluid flow in the horizontal cross-sectionprojection of the column through their structure.
 36. Internal membersaccording to claim 35, wherein the packing elements which create apreferred direction of flow are rotated 90° to one another around acolumn axis.
 37. Internal members according to claim 30, wherein a mainpacking part consists of packing blocks of the packing type of saidfirst packing block, said main packing part having a height that exceedsthe packing height of a correction packing part which consists ofpacking blocks of the packing type of said second packing block. 38.Internal members according to claim 37, wherein said main packing partis six to ten times as high as said correction packing part.